My good friend Ben, who happens to be an amazing microbiologist, offered to share some tips on how to choose the right ingredients to make DIY cosmetics safe, like my bath soak and sugar body scrub. I have a homemade lip balm that follows these rules coming up later this week. So without further ado, here’s Dr. Ben!

Four Simple Tips to Help Keep Homemade Cosmetics Safe – Written for ElizaDomestica.com by Benjamin Tanner, Ph.D., President of Cosmetic Test Labs

Making cosmetics and other personal care products at home is fun, rewarding, and economical.

One thing many people don’t know is cosmetics can be a breeding ground for germs. This is the reason professional cosmetics formulators often include preservatives; preservatives make sure cosmetics don’t pose an infection risk through the course of normal use.

To help keep DIY cosmetic projects safe, I have assembled a list of four simple tips along with an explanation of each.

Tip #1: Play it safe with ingredients

Professionals who evaluate ingredient safety, called toxicologists, have a saying: “The dose is the poison.” In other words, it’s not what a person consumes or contacts, it’s how much of a dose they get that determines whether or not they will fall ill.

Most people who make cosmetics at home don’t have the time or tools to figure out just how much of a potentially toxic ingredient can safely go into a cosmetic. For this reason, I recommend a common-sense approach to ingredient selection.

First, think about where the cosmetic will go. Will it go on skin, such as a salt scrub? Could it be ingested, such as a lip balm? Could it get into the eyes, such as an eyeshadow?

Once you know where the DIY cosmetic could wind up, make sure only to use ingredients you would comfortably put in or on that area of the body. For example, a lip balm made with honey, beeswax, and sunflower oil is OK because a person could safely eat all those things, but an eyeshadow made with vinegar is bad news, because vinegar could irritate or damage the eyes!

Tip #2: Use only fresh, high-quality ingredients

Many DIY cosmetics are made from around-the-house ingredients that are simply mixed together and applied to the body. Just like with food, these ingredients can start to grow microorganisms over time, and many have microorganisms in them even when fresh (like milk). Therefore, I recommend using the freshest ingredients possible.

Also, be on the lookout for low-quality ingredients. They might contain contaminants that simply don’t belong in a DIY cosmetic product. For example, grapefruit seed extracts from bad manufacturers was found to be contaminated with an irritating synthetic chemical called benzethonium chloride.

As a general rule, avoid uncooked animal products such as eggs in cosmetic formulations. They frequently contain low levels of dangerous microorganisms that can grow to dangerous proportions if not kept refrigerated.

Just as with food, one bad ingredient can spoil the final product. If you have any questions about the quality of a particular ingredient, it’s best to leave it out.

Tip #3: Heat cosmetics when possible to knock down germ levels

Many of the ingredients used to make DIY cosmetics, such as honey, cream, aloe vera, and eggs naturally contain microorganisms. Most microorganisms are harmless but some can definitely make a person sick and are sometimes found in food.

Heat is great at killing the microorganisms that make people sick. When choosing recipes for DIY cosmetics, pick those that involve heating the mixture before it’s finished. The end product will last longer and be more safe.

Tip #4: Set an “expiration date” and live by it

Most DIY cosmetics are made mostly from food ingredients. Unlike foods, some cosmetics come into direct contact with human skin, which is loaded with germs.

Depending on the person and the part of the body that comes into contact with the cosmetic, this can be a recipe for an unsafe product. DIY cosmetics lack the preservatives in off-the-shelf products that control germs introduced into products during normal use. Therefore, expiration dates are crucial to protecting the users of DIY cosmetics.

As a general rule, use the same time frames you would use for food. Most uncooked cosmetics should be used the same day they are made. If they’re refrigerated, they can be used for a few days.

Cooked cosmetics and concoctions with low amounts of water will naturally last longer, but remember that as soon as they are first used on the body, the clock starts ticking and they should be refrigerated if possible and thrown out a few days later. To avoid waste, make small batches, or make big batches and freeze them for later use.